1. Field of the Invention
This invention relates to a semiconductor device and a semiconductor device manufacturing method having a mounting process of mounting a semiconductor element on a substrate.
2. Description of the Related Art
Recently, the application field of semiconductor light emitting diodes (LEDs) has increased dramatically with the progress of the process technology associated with gallium-nitride (GaN) series compound semiconductor and the progress of the techniques associated with fluorescent bodies.
Particularly, since a semiconductor light emitting device having a combination of an LED which can emit light of a wavelength range of ultraviolet rays to visible light and a fluorescent body which is suitable for the LED can attain white light which is excellent in the color rendering property, the range of the application thereof to the backlight of the liquid crystal display, button illumination, various lights of cars and the like is further enlarged. In addition, a high-power semiconductor light emitting device used as a light source for a flash lamp, a flash of a camera and the like has been developed.
Recently, new packages which are each configured by mounting a plurality of LED chips in one package as shown in FIG. 10 are commercialized. The package is obtained by die-mounting a plurality of chips 200 on a ceramic substrate 100.
When the LED chips 200 with the junction-down structure are die-mounted on the ceramic substrate 100, the roughness of an electrode surface 101 of the ceramic substrate 100 cannot be compensated for by use of a solder film 102 (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 2003-234482) with the film thickness of 2 to 3 μm which is conventionally used since the electrode surface 101 of the ceramic substrate 100 is approximately 3 to 7 μm in Rz and rough. Thus, inadequate bonding may occur.
In order to solve the above problem, a method for setting the thickness of the solder film 102 substantially equal to the roughness of the electrode surface 101 of the ceramic substrate 100 is considered. However, since the surface roughness of the ceramic substrate 100 varies, there occurs a problem that molten solder is forced out from a gap between the ceramic substrate and the LED chip and is brought into contact with the side surface of the LED chip when the LED chip 200 is die-mounted on the electrode surface 101 having small variation in the surface roughness.
In order to solve the above problems, as shown in FIG. 12, a mounting method in which the film thickness of a bonding portion is increased by using Au—Sn solder paste 110 as a sub-member is studied. In the mounting method, first, Au—Sn solder paste 110 is supplied to an electrode surface 101 of the ceramic substrate 100. Then, LED chips 200 each having an Au—Sn solder film 102 formed on the bonding electrode are mounted on the Au—Sn solder paste. After this, the ceramic substrate 100 and LED chips 200 are passed through a reflow furnace to melt the solder portion. Since the mounting method is a reflow heating system, the LED chip 200 is lifted due to the surface tension of the solder, and therefore, the solder is prevented from creeping up to the side surface of the LED chip 200.
However, in a solder bonding method of forming an Au—Sn solder film 102 on the die-mount bonding surface of the LED chip 200 and supplying Au—Sn solder paste 110 as a sub-member, there occurs a problem that air bubbles 111 will often occur in the bonding portion.